Unfortunately we've seen reports of counterfeit product from online purveyors; there currently are no regulations and some of these medications may have been acquired through means that are difficult to track; sometimes they are past their expiration date as well. I would be very wary of the company that you cite.

Pets should be tested yearly because there have been recent studies that indicate heart worm can be resistant to some preventatives, and so a full exam by a veterinarian is the best chance to accurately diagnose heart worm, and begin the most effective treatment program.I hope that's helpful.

PS - yes, the warmer weather this winter means that many pests (mostly ticks) are still a concern for pet owners. Check your dog regularly for ticks and please use a tick preventative throughout the winter months, just to be safe.